1. Field of the Invention
This invention relates to an aromatic polysulfone resin composition exhibiting high heat resistance, superior mechanical properties, low mold shrinkage, and good mold releasability.
2. Description of the Prior Art
Aromatic polysulfone resins are noticed as engineering plastics superior in heat resistance, strength, stiffness, flame resistance, chemical resistance, processability, etc., particularly in the fields of applications to electric parts and automotive parts.
In these application fields, however, there is a growing need, with technical progress in these fields, for an aromatic polysulfone resin composition having higher heat resistance, stiffness, and dimensional accuracy (low mold shrinkage) while maintaining the flame resistance, chemical resistance, hot water resistance, and processability which are merits of this resin.
It is known that the heat resistance, stiffness, and dimensional accuracy of resins are improved, as a rule, by incorporating thereinto a fibrous reinforcement such as glass fiber, carbon fiber, or the like or an inorganic filler in powdery acicular, or flaky form, such as talc, calcium carbonate, magnesium carbonate, calcium sulfite, aluminum hydroxide, mica, molybdenum disulfide, wollastonite, graphite, titanium white, or glass beads.
Also when aromatic polysulfone resin is compounded with such a reinforcement or filler, improvements in the heat resistance and stiffness and a decrease in the mold shrinkage are observed responsively to the quantity of the reinforcement or filler blended.
With the increase of quantity of the reinforcement or filler blended, the mold shrinkage decreases and the mold fidelity in injection molding and in similar molding becomes better; but the mold releasability in injection molding lowers and the take-off of the molded article from the mold cavity becomes difficult. In consequence, excess stress is exerted on the molded article when it is ejected from the cavity; this leaves strain in the molded article and may cause troubles such as the deformation of the molded article at the time of the ejection and the stress cracking and eventual break of the finished article.
Accordingly, in spite of the strong request for a resin composition exhibiting low mold shrinkage and excellent mold fidelity and dimensional accuracy, the quantity of the reinforcement or filler to be blended is usually restricted so as to hold the reduction of the mold shrinkage in such a degree that none of the above problems arise in the operation of releasing the molded article from the mold cavity.
In view of the above, the present inventors made intensive studies, and as a result, found that a resin composition which has high heat resistance, stiffness, and strength and exhibits low mold shrinkage and good mold releasability can be obtained by compounding an aromatic polysulfone with a fibrous reinforcement or an inorganic filler and additionally with a specified amount of a fluororesin. Based on this finding, this invention has been accomplished.